1. Field of the Invention
The present invention relates to movable or adjustable platforms and to tripods, and particularly to a kinematic platform having three legs providing six degrees of freedom with controlled braking at each joint and high dexterity within the workspace.
2. Description of the Related Art
A need exists for simple and effective parallel kinematics mechanisms. Kinematics mechanisms are used in mechanical engineering applications for machining, robotics, positioning devices, coordinate measuring, fixtures, etc. Serial kinematics mechanisms are widely used and presently dominate the market. A serial kinematics mechanism has a series of cantilever beams that are movably connected together in an end-to-end fashion by prismatic, revolute or spherical joints, forming an open loop. The closer that a member is to a base of the mechanism within the serial structure, the higher the load on that member. Additionally, the farther that a member is from the base, the higher its deflection with respect to the base member. When a serial kinematics mechanism is subjected to loading, the position of the farthest member; i.e., the end-effector, is subject to the cumulative deflections of all serial members. Unfortunately, this results in large positioning errors at the end-effector. Being constructed of cantilevers, a serial mechanism has a poor stiffness to mass ratio, making such structures bulky in design with difficult in control of the joints.
Serial kinematics mechanisms allow fast and easy computation of the position of the end-effector given the position or state of all actuators. In general, this computation is known as the forward kinematics of a mechanism. However, determining the position or state of all actuators given the position of the end-effector, also known as the inverse kinematics, is very difficult. Particularly, control over rotation of the joints is of primary concern in serial kinematic platforms.
Numerous ball and socket joints having manual joint locking mechanisms exist. Such mechanisms are usually very complex and due to the manual locking are not suitable for robotic or parallel kinematic machine operations. Even lockable joint devices linked to hydraulic systems may not be suitable for robotic applications, or the like. Moreover, ball joints with detent stopping action do not lock to an arbitrarily desired position, and therefore are not precise enough for robotic machine applications. It would be very desirable to overcome the aforementioned problems caused by the use of existing ball joint mechanisms. Thus, a kinematic platform solving the aforementioned problems is desired.